<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .bigbox {
        width: 800px;
        height: 100px;
        margin: 0px auto;
        text-align: center;
    }

    #box1 {
        width: 150px;
        line-height: 300px;
        background: #0c68d5;
        border: 1px solid #eaeaea;
        border-radius: 5px;
        color: #fff;
        cursor: pointer;
        font-size: 24px;
    }

    .HTML {
        color: #fff;
        font-size: 100px;
        line-height: 200px;
        font-weight: 900;
        animation: identifier;

    }
</style>

<body>
    <div class="bigbox" style="z-index: 99;">
        <button class="btn" id="btn1">dianji</button>
        <div class="HTML" id="box1">
            <p>btn被点击</p>
        </div>
    </div>
    <script>
        window.onload = function () {
            var Btn1 = document.getElementById("btn1");
            var box1 = document.getElementById("box1");
            Btn1.onclick = function () {
                o = setTimeout(function () {
                    Btn1.onclick();
                }, 3000);
                var a =1 
                box1.innerHTML = "<P>btn1被点击</P>" + a;
                a = a + 1;
            }
        }
    </script>
</body>

</html>